At which points in a one-way, multiple hop, end-to-end IP communications session will a frame have to be built?

In a one-way, multiple hop, end-to-end IP communications session, a frame must be built at two key points: at the sending host's LAN port and at each hop's router outbound port.

At the sending host's LAN port, a frame is initially constructed to encapsulate the IP packet for transmission over the local network. This includes adding the necessary MAC (Media Access Control) address of the next hop (usually the router) and other link-layer information.

As the data travels through the network, it reaches intermediate routers that are responsible for forwarding the packets towards the final destination. When the packet arrives at each router, the router processes the incoming packet and then needs to forward it to the next hop. To do this, the router constructs a new frame at its outbound port. This new frame encapsulates the packet with the MAC address of the next hop (which could be another router or the final destination host) and prepares it for transmission on the link to that next hop.

Thus, both the sending host's LAN port and each router's outbound port are critical points where frames are built in a multi-hop communication scenario.